It is known to provide a fuel level sensor in a fuel tank of a vehicle to sense or indicate a level of fuel in the fuel tank. One type includes a float connected to an arm that moves an electrical contact, changing resistance in response to fuel height. The fuel level sensor may include a ceramic resistor card operatively connected to a structure for a fuel module and a wiper assembly pivotally connected to the structure for engaging the resistor card. The wiper assembly has one end connected to a float arm and float to rotate the wiper assembly relative to the resistor card based on a level of fuel in the fuel tank.
In this regard, one type of such a fuel level sensor employs thick film ceramic fuel level sensors that are open and exposed to fuel in the fuel tank. These fuel level sensors typically employ silver (Ag) based conductive inks (Ag, Pd, Pt) and high content Ag contacts. These materials function properly in fuels that contain moderate sulfur levels or that are low in alcohol content. These materials have also allowed manufacturers to produce a cost effective fuel level sensor.
Fuel level sensors that are open and exposed to fuels have, however, been susceptible to solid contaminates, for example sand, which can cause the sensor output to produce opens. As sulfur levels in fuels are reduced, what remains are smaller, more reactive compounds. Sulfination is a chemical reaction between Ag and sulfur. Natural aging of the ink/contact interfaces of the fuel level sensor exposes the silver in these components to sulfurs, producing a thin lacquer contamination. Silver based fuel level sensors produce opens or a shift in resistance when exposed to this extremely reactive fuel.
Also, as refineries introduce fuels with higher levels of alcohol, silver based fuel level sensors that are open or exposed to this fuel are more susceptible to plating, galvanic, or dendritic growth. Accordingly, this type of float-based fuel level sensor is subject to not only mechanical wear through abrasion but to fuel contamination as well, and must be sealed somehow for use in aggressive fuels (e.g., higher levels of alcohol and/or sulfur).
One approach taken in the art involves providing a sealed cavity for housing and protecting the variable resistor from the influences of aggressive fuels and contaminants, as seen by reference to U.S. Patent Application Publication No. US 2006/0042379 A1 entitled “SEALED FUEL LEVEL SENSOR” to Ireland et al., owned by the common assignee of the present invention. This wiper-type fuel level sensor may nonetheless be subject to mechanical wear.
Another type of fuel level sensor employs any of several schemes to measure fuel level without moving components, such a through the use of dielectrics or ultrasound measurement. This type of sensor involves the use of conductive inks screened onto relatively long substrates, in the case of the dielectric units, and includes complex transmitters and receivers in the case of ultrasonics. Both of these units have complex electronics that have to be packaged outside the fuel tank, or provided in a sealed enclosure for use in the fuel tank to operate properly.
There is therefore a need for an improved fuel level sensor that minimizes or eliminates one or more of the problems set forth above.